...are we missing something here? Are you running a 261 with a 235 head?? I'm putting together a 261 and just had the 235 head drilled with the extra holes to match the 261 block.
You stated "I know about drilling holes in the thermostat to keep water flowing and prevent hot spots from forming." As Joe H. mentioned the small hole in the thermostat is to let the air out....but the holes we drill in the 235 heads for a 261 are, as you say, to "prevent hot spots".
I was just a little confused but that's not hard for me to be!!!
...kudos, for trying to make things better.
I'm sorry if I confused anyone with my opening statement about my 261. I am building a 261 with a 235 head (although right now it is a pile of parts in my shop) and it does have the appropriate steam holes drilled in the head surface. Those steam holes will do no good if there is no water flow through the engine like when the thermostat is closed. That's why GM put a bypass type thermostat on 261's. The components for the 261 bypass thermostat are hard to come by and when the discussion comes up about what to do about it someone usually suggests drilling holes in a regular thermostat. This not only bleeds air out of the system as JoeH stated but it also keeps some coolant flow through the engine to prevent hot spots from developing. Although it takes more than a single 1/8" hole for this purpose.
By the way, some aluminum radiator manufacturers recommend drilling (3) 1/8" holes in the thermostat to prevent damage to the radiator from thermal shock. If hot water from the engine can damage the radiator then cold water from the radiator can't be good for the engine. It works both ways.
The example I gave about the temperature fluctuations I have seen are on the 235 that is currently in my truck. There is nothing wrong with it that causes these fluctuations. It works as well as it did in 1958 and after a few temperature swings it levels off and runs right on the thermostat. The condition I described is inherent in most internal combustion engines, but is exaggerated in stove bolts because of the thermostat location. Thing is most people aren't aware of it and because the effects are long term most people don't care.
The effect is probably lessened with a thermostatically controlled electric fan since you are not removing as much heat from the radiator when there is no coolant flow. I have a very efficient aluminum radiator, mechanical fan, and shroud so I am chilling the water at all times. And no I don't want to use an electric fan. (before someone suggests it)
I guess my original question has been answered since no one knows what I am talking about. I am going to do it so if anyone is interested I will show the process and the results.
